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The overall goal of this study was to develop warrants or guidelines for the installation of active warning devices without speed selection (fixed-distance systems) and active warning devices with speed selection (constant warning time systems) at railroad highway grade crossings. This objective was achieved by the use of the FRA grade crossing inventory and accident data bases to develop accident rates, effectiveness values, statistical models to determine which variables are significantly related to accidents, and a benefit cost analysis, all of which were used in warrant development. Overall results of this study tended to confirm the hypothesis that constant warning time systems have greater credibility with motorists than do fixed-distance systems. The effectiveness values for changes from fixed-distance to constant warning time systems confirmed this. Accident rates for both fixed-distance and constant warning time systems were developed and showed that on the average, constant warning time systems tended to have lower rates. A separate regression technique showed that the only two variables that were significantly related to accident rates were warning device types and exposure. In general, constant warning time systems were warranted at a higher exposure level than fixed-distance systems. Keeping the cost ratio fixed, flashing lights of fixed distance are warranted at the least exposure level for crossings formerly equipped with passive devices, followed by flashing lights of constant warning time, gates of fixed distance and last, gates of constant warning time. For crossings formerly equipped with gates of fixed distance, gates of constant warning time will rarely be warranted.